1. Field of the Invention
The present invention relates to a gas generator or inflator that utilizes the combustion of a solid fuel gas generant composition for the generation of a gas for rapidly inflating a vehicle passive restraint inflatable crash protection bag, and more particularly, to the assembly in such an inflator of an ignition squib or initiator.
2. Description of the Prior Art
A variety of gas generators or inflators that utilize combustible solid fuel gas generant compositions for the inflation of an inflatable crash protection or "air bag" restraint system are known in the prior art. Typical forms of such inflators utilizing ignition squibs for the initiation thereof are disclosed in the following U.S. patents:
______________________________________ U.S. Pat. No. Issue Date Patentee ______________________________________ 3,951,428 April 20, 1976 Fumio Sigura et al. 3,986,456 Oct. 19, 1976 Bernard J. Doin et al. 4,116,466 Sept. 26, 1978 Robert G. Gehrig 4,131,299 Dec. 26, 1978 Koichi Ono et al. 4,249,673 Feb. 10, 1981 Masayoshi Katoh et al. 4,278,638 July 14, 1981 Karl E. Nilsson et al. 4,296,084 Oct. 20, 1981 Gary V. Adams et al. 4,547,342 Oct. 15, 1985 Gary V. Adams et al. 4,561,675 Dec. 31, 1985 Gary V. Adams et al. ______________________________________
Gas generators or inflators must withstand enormous thermal and mechanical stresses for a short period during the gas generation process. As a result, inflators have been fabricated using steel for the casing and other housing structural components, with the structural components being joined together by screw threads, roll crimping or welding, and with the initiator or ignition squib assembled prior to joining the structural components in some cases, and after, in others. Where the initiator is assembled after joining of the structural components, it has been the practice to screw the initiator into a tap hole in the external steel casing, as disclosed, for example, in the aforementioned U.S. Pat. Nos. 3,951,428; 3,986,456; 4,249,673 and 4,131,299.
Emphasis on weight reduction in automobiles has created a need for lighter weight crash bag inflation systems. This is of particular importance in a system for driver crash bag protection where the inflator is mounted on the steering wheel. Specifically, the availability of a lighter weight inflator enables a reduction to be made in the weight of the steering wheel and steering column on which the inflator is mounted.
It has been determined that the most significant weight reductions in the inflator can be achieved by the substitution of aluminum for the steel casing and other housing structural components, aluminum already being used internally in the inflator as containers, seals and filter media. Such light weight inflators in which aluminum has been substituted for steel in the casing and other structural components are disclosed in the above-mentioned Adams et al. U.S. Pat. Nos. 4,547,342 and 4,561,675. The inflator of each of these patents includes first and second aluminum structural components. The first component, a diffuser shell having outlet ports, includes three integrally formed concentric cylinders which define chambers containing ignition materials, a solid gas generant composition and filters and provide ports for the passage of generated gases from chamber to chamber and then through outer ports. The second component, a base shell, includes an ignition squib or initiator captured therein and is provided with three concentric surfaces that mate with the ends of the concentric cylinders of the first component. The three concentric cylinders of the diffuser shell component are simultaneously joined with the base shell initiating surfaces of the second component by a single inertia welding operation.
While the manner of assembly and performance of the captured ignition squib or initiator in the aluminum inflator of each of U.S. Pat. Nos. 4,547,342 and 4,561,675 are satisfactory, there are problems in respect of complexity, space required to capture and lock the ignition squib in place, and a requirement for the assembly of the ignition squib in the inflator before the diffuser shell and base shell components are welded together.
The use of a tap hole having an internal screw thread in the aluminum base shell of the inflator for enabling the ignition squib to be assembled after the welding operation and assembly of the pyrotechnics also presents a problem. This is for the reason that while such a tap hole is satisfactory for use in a steel casing, it is not satisfactory for use in an aluminum base shell as employed in the inflator of U.S. Pat. Nos. 4,547,342 and 4,561,675. A tap hole in such an aluminum base shell would require a much larger thread than that suitable for steel casings in order to carry the load, and hence, a correspondingly larger space to lock the ignition squib in place.
Thus, there exists a need and a demand for improvement in the method of and apparatus used to incorporate the ignition squib in the casing or housing of a gas generator or inflator after the structural components thereof have been joined together and the inflator pyrotechnics have been assembled therein. There is a particular need and demand for facilitating the assembly of the ignition squib in the base shell of an aluminum inflator, as above described, after the welding operation and assembly therein of the inflator pyrotechnics.